The invention relates to a method for producing a bevel on the edge of a spectacle lens using a CNC-controlled spectacle-lens edge-machining machine.
EP 0 706 439 B1 by the same applicant describes a method and an apparatus with which changes in the bevel because of the wear to a grinding wheel used for producing the bevel can be taken into consideration.
During the grinding of a bevel on spectacle lenses, wear to the grinding wheel arises in the bevel groove, the wear not only leading to a slow increase in the size of the finish-ground spectacle lenses, but also to an increase in the size of the angle of the bevel, i.e. to a flattening. The flattening of the bevel can be accepted to a certain degree as long as the spectacle lens is securely held in the bevel groove of the spectacle frame concerned. In order to achieve this, it is proposed according to EP 0 706 439 B1 to subject the spectacle lens, which has been ground around the circumferential contour, to a correction grinding which takes the flattening of the bevel into consideration. For this purpose, the spectacle-lens edge-machining machine has, adjacent to the grinding wheel, a support having a wedging groove whose wedge angle corresponds to a permissible, maximum angle of a bevel on the spectacle lens. If the spectacle lens, ground into shape and provided with a bevel, is inserted into the wedging groove, a measured value which is exclusively dependent on the radial wear of the grinding wheel is produced, as long as the angle of the groove of the shape-ground spectacle lens does not exceed the angle of the wedging groove on the support.
Until angle parity has been reached, its suffices to undertake a correction grinding which corresponds to the linear difference in radius. If the wear to the grinding wheel used for the bevel grinding is so great that the angle of the ridge bevel is greater than the angle of the wedging groove on the support, the spectacle lens to be measured can no longer enter with its ridge bevel completely into the wedging groove, so that a greater difference is measured than corresponds to the linear change in diameter of the grinding wheel. In this case, the spectacle-lens edge-machining machine can end the grinding procedure and output a signal which indicates to the operator that the grinding wheel has to be trimmed and has become unusable.
In order to ascertain whether the angle of the bevel on the shape-ground spectacle lens has exceeded a predetermined value, the support has a flat region in addition to the wedging groove, and at least one radius value for the tip of the bevel in the wedging groove and a further radius value with regard to the flat region are recorded. It can then be determined from the difference in these values in comparison to a desired value whether or not the change still lies within permissible limits.
The method and the apparatus disclosed in EP 0 706 439 B1 have been tried and tested, but require an additional correction grinding if there is a change to the bevel groove or to the diameter of the grinding wheel which requires correction. Also, it can only be ascertained that the grinding wheel has to be trimmed and has become unusable if a spectacle lens which has already been ground into shape is being measured on the support. Furthermore, in the case of the known method and apparatus the cross-sectional shape of the bevel groove in the spectacle frame, for which the spectacle lens which is to be ground into shape is intended, is not taken into consideration during this test procedure.
The invention is therefore based on the problem of providing a method and an apparatus for producing a bevel on the edge of a spectacle lens, using which the wear to a bevel groove in a spectacle-lens edge-machining tool is checked before the machining of the spectacle lens is carried out, and using which it is also possible to take into consideration the shape of the bevel groove in a selected spectacle frame.
Taking this problem as the starting point, a method for producing a bevel on the edge of a spectacle lens using a CNC-controlled spectacle-lens edge-machining machine is proposed comprising, according to the invention, the following steps: scanning the bevel groove of a spectacle-lens opening in a selected spectacle frame, including the cross-sectional shape and the circumference of the bevel groove, inputting the determined values into a control device of the spectacle-lens edge-machining machine, scanning the spectacle-lens edge-machining tool with regard to its diameter and the shape of its bevel groove, inputting the determined values into the control device of the spectacle-lens edge-machining machine, comparing the values of the cross-sectional shape of the bevel groove of the spectacle frame with the values of the cross-sectional shape of the bevel groove of the spectacle-lens edge-machining tool, carrying out the machining of the bevel using the determined values, if the compared values of the cross-sectional shape and the diameter of the spectacle-lens edge-machining tool lie within a predeterminable first tolerance range, or carrying out the machining of the bevel using a correction value, if the compared values of the cross-sectional shape lie within a second tolerance range and/or the diameter of the spectacle-lens edge-machining tool is smaller than a predeterminable minimum value, or breaking off the machining of the bevel, if the compared values lie outside the first and second tolerance range.
The invention is based on the consideration that, firstly, with regard to their cross-sectional shape the bevel grooves in the spectacle frame lie within a tolerance range, the cross-sectional shape of the bevel groove being determined by the depth of the bevel groove and the angle enclosed by the flanks of the bevel groove. The depth of the bevel groove and the flank angle and also the diameter of the spectacle-lens edge-machining tool can move within a permissible tolerance range.
Secondly, a new, unused spectacle-lens edge-machining tool has a bevel groove which can be produced very precisely with exacting tolerances. However, during the grinding of the bevel of a spectacle lens, wear to the spectacle-lens edge-machining tool with regard to its diameter and the cross-sectional shape of the bevel groove arises, the wear not only leading to an increase in the size of the finish-ground spectacle lens, but also to an increase in the size of the angle of the bevel, i.e. to a flattening.
If a comparison between the actual state of the bevel groove in the spectacle frame and that of the bevel groove in the spectacle-lens edge-machining tool is carried out, in many cases despite wear to the bevel groove having been ascertained and possibly after undertaking a correction during the production of the bevel, the spectacle-lens edge-machining tool can continue to be used if the cross-sectional shape of the bevel groove in the spectacle frame permits this. In this case, a reduction in the diameter of the spectacle-lens edge-machining tool can be taken into consideration by correcting the feed motion of the spectacle lens with regard to the spectacle-lens edge-machining tool.
Since the scanning of the bevel grooves in the spectacle frame and in the spectacle-lens edge-machining tool is carried out before the spectacle lens is machined into shape and provided with a bevel, additional correcting steps are not required, rather any correction required is included by computation in the data record for the CNC-controlled machining of the spectacle-lens edge, so that the spectacle-lens edge machining directly delivers a spectacle lens which is suitable for the selected spectacle frame, has been ground to shape and is provided with a bevel.
The scanning of the bevel grooves in the spectacle frame and in the spectacle-lens edge-machining tool can preferably be carried out in a contactless manner by means of video-scanner systems, and the cross-sectional shape of the bevel groove can be reproduced on a viewing screen. An apparatus for the contactless scanning of the bevel grooves in spectacle frames by means of a video-scanner system is described in DE 40 19 866 A1 by the same applicant. However, laser-scanner systems are also suitable.
The first tolerance range, which permits the machining of the bevel to be carried out using the determined values without including a correction value, may cover an angular range of the bevel groove of the spectacle frame, which is equal to or greater than the angular range of the bevel groove of the spectacle-lens edge-machining tool, may cover a depth range of the bevel groove of the spectacle frame, which is equal to or smaller than the depth range of the bevel groove of the spectacle-lens edge-machining tool, and may cover a diameter range of the spectacle-lens edge-machining tool, which is equal to or smaller than the desired diameter of the spectacle-lens edge-machining tool.
The second tolerance range, which permits the machining of the bevel to be carried out with a correction value being included, may cover an angular range of the bevel groove of the spectacle frame, which is smaller than or equal to the angular range of the bevel groove of the spectacle-lens edge-machining tool, in which the maximum value of the angle of the bevel groove of the spectacle-lens edge-machining tool must not exceed a predeterminable value, and the correction value is determined from the depth of penetration, which can be calculated from the actual angles of the bevel grooves of the spectacle frame and of the spectacle-lens edge-machining tool, of the bevel on the shape-ground spectacle lens into the bevel groove of the spectacle frame, in such a manner that the spectacle lens is machined smaller by a radial value which corresponds to the distance between the bevel tip on the spectacle lens and the base of the bevel groove of the spectacle frame. A further correction value may, if required, be determined from the reduction in diameter of the spectacle-lens edge-machining tool.
If the compared values lie outside the first and the second tolerance range, the machining of the bevel is broken off, specifically if it turns out that the angle and the depth of the bevel groove of the spectacle frame are greater than the angle and the depth of the bevel groove of the spectacle-lens edge-machining tool, or if the angle of the bevel groove of the spectacle-lens edge-machining tool is greater than a predeterminable maximum value.
A spectacle-lens edge-machining machine which is suitable for solving the problem mentioned at the beginning can have at least one spectacle-lens edge-machining tool with a bevel groove, a rotable spectacle-lens holding shaft which is at least radially adjustable relative to the spectacle-lens edge-machining tool, a control device controlling the spectacle-lens edge-machining machine, an apparatus which is connected to the control device and is intended for scanning the bevel groove of the spectacle-lens edge-machining tool with regard to diameter and cross-sectional shape and circumference, an apparatus which is connected to the control device and is intended for scanning the bevel groove of a spectacle-lens opening in a selected spectacle frame, including the cross-sectional shape, a comparison device in the control device for comparing the values of the cross-sectional shape of the bevel groove of the spectacle frame with the values of the cross-sectional shape of the bevel groove of the spectacle-lens edge-machining tool, and a device for controlling the implementing of the bevels using the determined values, if the compared values of the cross-sectional shapes and of the diameter of the spectacle-lens edge-machining tool lie within a predeterminable first tolerance range or the carrying out of the machining of the bevel using a correction value, if the compared values of the cross-sectional shapes lie within a second tolerance range and/or the diameter of the spectacle-lens edge-machining tool is smaller than a predeterminable minimum value, or the breaking off of the machining of the bevel, if the compared values lie outside both tolerance ranges.
The apparatuses for scanning the bevel groove in the spectacle-lens edge-machining tool and in the spectacle frame may preferably consist of contactless video-scanner systems, which particularly preferably comprise CCD cameras.
These CCD cameras supply data which are digitized via an image-evaluating system in the control device and with the aid of which the comparison of the bevel grooves of the spectacle frame and of the spectacle-lens edge-machining tool can be carried out under computer control, and which enable the bevel groove of the spectacle-lens edge-machining tool and of the spectacle frame to be reproduced on a viewing screen.
However, laser-scanner systems are likewise suitable.
With the aid of the image-evaluating system and a corresponding computer program in the control device, it is furthermore possible for the bevel groove of the spectacle frame and, inserted therein, a bevel of a spectacle lens, corresponding to the bevel groove of the spectacle-lens edge-machining tool, to be reproduced on the viewing screen, so that it can be seen directly on the viewing screen whether the machining of the bevel can be carried out without inserting a correction value, with a correction value or not at all.
However, this representation is used only for information for the operator, since the machining of the bevel is carried out by means of the control device under fully automatic control in accordance with the criteria mentioned above.